Swift可选链

//可选链测试
 
class Person{
 
    var residence:Residence!
 
    var name:String
 
    init(name:String){
 
        self.name = name
 
    }
 
}
 
///住宅
 
class Residence {
 
    var residenceNum = 101
 
}
 
var lucy = Person(name: "Lucy")
 
//没有为lucy初始化住宅
 
if let roomNumber1 = lucy.residence?.residenceNum {
 
    print("\(lucy.name)有住宅,住宅号是\(roomNumber1)")
 
}else{
 
    print("\(lucy.name)没有住宅")
 
}
 
var lily = Person(name: "Lily")
 
lily.residence = Residence()
 
if let roomNumber2 = lily.residence?.residenceNum {
 
    print("\(lily.name)有住宅,住宅号是\(roomNumber2)")
 
}else{
 
    print("\(lily.name)没有住宅")
 
}

//1.可选链的访问方式:将强制解析的感叹号换成?,在隐式解析的后面也添加?后缀

//2.可选链会自动判断程序访问的关联实例是否为nil